The present invention relates to thermal exchangers and more specifically to thermal exchangers capable of delivering a sample solution at a specified temperature to a detector for liquid chromatography systems.
Liquid chromatography systems are well known for analyzing sample solutions made up of different chemical compounds. Typically, a liquid chromatography system includes a chromatography column packed with packing material, a detector for analyzing the sample solution, a section of tubing for carrying the sample solution from the chromatography column to the detector, and a section of tubing for carrying the sample solution from the detector and out of the chromatography system.
The operation of a liquid chromatography system can be generally described as follows. A liquid solvent is pumped into the chromatography system at high pressure. At a point in the chromatography system ahead of the chromatography column, the sample solution is injected into the system and carried forward with the liquid solvent. Eventually, the sample solution reaches the packed chromatography column and begins to flow through it. Because each of the chemical compounds which make up the sample solution reacts differently with the packing material in the chromatography column, the various chemical compounds flow through the packed column at different rates. Thus, the different chemical compounds in the sample solution separate out as individual peaks in concentration as the sample solution flows through the chromatography column. From the packed chromatography column, the separated chemical compounds proceed to the detector where they are analyzed. In the detector, some physical characteristic of the compounds is measured to identify the chemical composition of the peaks in the liquid solvent.
One type of detector utilized in liquid chromatography systems is a refractive index detector. Refractive index detectors measure the difference in refractive index of a two fluids and typically consist of a light emitting diode (LED), a flow cell having a sample side and a reference side, and a dual element photodiode detector. The refractive index of a fluid is highly dependent on the temperature of the fluid. Even slight variations in the temperature of a fluid drastically affect the refractive index of the fluid. For this reason, refractive index detectors are often fitted with temperature-controlled ovens within which the above detector elements reside. The oven is typically set to a temperature higher than the ambient temperature or surrounding environment temperature to insure control within narrow limits.
Often times, the sample solution exits the packed chromatography column at temperatures significantly higher or lower than the detector oven temperature. Because the refractive index of a fluid is so highly dependent on the temperature of the fluid, liquid chromatography systems that utilize refractive index detectors or other similar detectors must include special heat exchangers in order to provide meaningful results. The special heat exchangers insure the sample solution received by the refractive index detector is at a stable temperature within narrow limits. The present invention is a special tube-in-tube heat exchanger which uses fluid counterflow to exchange thermal energy between the incoming sample solvent and the outgoing waste solvent. This exchange of thermal energy automatically raises or lowers the temperature of the incoming sample fluid to a value very close to that of the detector oven. Outgoing fluid is already at the same temperature as that of the oven and provides the proper amount of thermal energy to the incoming fluid. In this way, the incoming fluid can more easily be stabilized to the exact oven temperature by the next stage heat exchanger attached to the optical bench assembly inside the detector oven.
In addition to insuring the sample solution is presented to the detector at a stable temperature, a heat exchanger utilized in a liquid chromatography system that includes a refractive index detector or other similar detector must introduce minimal volume into the flow path between the chromatographic column and the detector. If the heat exchanger introduces too much volume into the flow path between the chromatography column and the detector, there is a high probability that the constituent compound peaks that were separated in the chromatography column will be distorted and made less distinct. To the extent any previously separated compound peaks are made less distinct, the performance of the liquid chromatography system is adversely affected.
Thermal exchangers like the one disclosed in U.S. Pat. No. 4,284,352 entitled xe2x80x9cHeat Exchanger for Refractometerxe2x80x9d issued to Carson have been used previously in liquid chromatography systems. The Carson thermal exchanger is less than ideal for several reasons. One major problem with the Carson exchanger is that it is very difficult to manufacture, Four steps are required to manufacture the heat exchanger. First, four stainless steel tubes must be formed into a bundle. Second, the bundled tubes must be lashed or wrapped together with wire. Third, the tube bundle must be plated with copper so that the stainless steel tubes will accept solder. And fourth, the plated tubes must be dipped in solder to form a thermal contact path among the tubes.
An additional problem with the Carson heat exchanger is that it cannot be modified or repaired once it is manufactured. The heat exchanger is a permanent soldered assembly. If one of the tubes breaks or get clogged, the entire heat exchanger must be replaced.
The present invention provides a thermal exchanger capable of providing a fluid whose temperature has been brought very close to that of a desired stable temperature setpoint within a detector. The thermal exchanger introduces minimal volume into the flow path between the chromatography column and the detector. The thermal exchanger of the present invention is easy to manufacture, repair and it is modifiable.
According to the present invention, in a liquid chromatography system including a chromatography column packed with packing material and a detector, a thermal exchanger comprises a first and second section of tubing, a waste T connector and a sample T connector. The first section of tubing carries sample solution from the packed chromatography column. The second section carries the sample solution from the detector out of the system. Both the first section of tubing and the second section of tubing connect to the first T connector. From the first T connector, a third section of tubing emerges. The third section of tubing comprises the first section of tubing placed inside the second section of tubing such that waste fluid can exchange thermal energy with fluid from the chromatography column. The third section of tubing is wrapped into a plurality of coils. The number of coils in the third section of tubing depends on the specific chromatography application. The present invention provides a thermal exchanger capable of adjusting a high or low temperature incoming fluid to a stable temperature close to a desired temperature at a detector. The present invention also introduces minimal volume into the flow path between the chromatography column and the detector.
An advantage of the present invention is its ability to deliver sample solution at a desired, stabilized temperature to a detector where the sample solution is analyzed.
A minimal amount of additional volume is introduced into the flow path between a chromatography column and a detector. Another advantage of the present invention is that it is easy to manufacture, repair and it is modifiable.
Another advantage of the thermal exchanger according to the present invention is that it provides optimal thermal contact between sample solution coming into the chromatography system and sample solution exiting the sample solution.